Final answer:
True primates, or euprimates, first appeared about 55 MYA in the Eocene epoch, resembling modern-day prosimians and showing significant evolutionary changes towards larger brains and eyes.
Step-by-step explanation:
The first true primates, known as euprimates, appeared approximately 55 million years ago (MYA) during the Eocene epoch. These early primates are believed to have resembled modern-day prosimians, such as lemurs. They have been found in North America, Europe, Asia, and Africa. The Eocene epoch is characterized by significant evolutionary changes, leading to primates with larger brains and eyes, and smaller muzzles. By the end of this time period, many prosimian species had gone extinct, possibly due to cooler temperatures or competition from the first monkeys that appeared in the Oligocene epoch.